Both clinical and research data have produced evidence that the cerebral hemispheres in man are not simply functional duplicates of each other, but are specialized to process information in different ways. Recent controversy has emerged as to whether this functional specialization is present at birth or whether it develops gradually during the early years of life. Previous evidence pertaining to cerebral specialization has largely come from studies of patients with lesions, patients with cerebral disconnection syndrome, clinical tests, such as the Wada test, and from various behavioral studies. More recently a number of investigations have used EEG methods in an attempt to directly measure differences in hemispheric function during specific tasks. These studies have focused on adults, and the results that have been obtained to date are inconclusive. The purpose of the proposed investigation will be to study, using EEG techniques, cerebral functional specialization as it largely pertains to the development of language. Two paradigms are proposed to study cerebral functional specialization in infants. The cortical evoked potential, elicited by speech and nonspeech stimuli, will be measured from both hemispheres while subjects are presented with tasks designed to activate specific cortical sites. Both longitudinal and cross-sectional studies are incorporated in this proposal. The proposed measures may provide useful information about the cognitive development of human infants.